Earlier in the previous section we’ve studied about SCHEDULE SERIALIZABILITY AND ITS TYPE . In this section we’ll continue about. SCHEDULE SERIALIZABILITY AND ITS TYPE in brief. SERIALIZABILITY is a concept that helps to identify which non serializable schedule are correct. And will maintain the consistency. In summary they behaves exactly as serial schedule. Thus these are always. Consistent. Cascade less. Recoverable strict.
TYPES OF SERIALIZABILITY:
- CONFLICT SERIALIZABILITY
- VIEW SERIALIZABILITY
CONFLICT SERIALIZABILITY:
If a given non serial schedule . Can be convert into serial schedule. By swapping its non-conflicting serializable schedule. Then it is call as conflict serializable schedule. In the meantime condition for conflicting operations are.
Both the operations belong to different transactions . Or Both the operations are on same data items. Or at least one of the two operation is write operation. In this topic questions of precedence graph are taken on practice.
VIEW SERIALIZABILITY:
If a given schedule. Found to be view equivalent. To some serial schedule. Then it is called as view serializability. Conditions for view serializability. If a schedule is conflict serializable . Then it must be view serializable. In case if it is not conflict serializable. We have to find blind write. If there are blind write. Then it can be in view serializable otherwise not. But in summary, though it is tough concept. Furthermore It is not that much in practice.
Now let’s study about lock-based protocols. In addition to achieve serializability and consistency. We use lock based protocols. These are of two types .
Shared lock
It is also known as Read-only lock. In a shared lock, only read is possible. Consequently it means data item can only read by the transaction.
EXCLUSIVE LOCK
In this lock. The data item can be both. Read as well as written by transaction.
DRAWBACKS IN SHARED/EXCLUSIVE LOCK
- May not sufficient to produce only serializable schedule.
- It may not free from irretrievability.
- May not be free from dead lock.
- It may not be free from starvation.
